Current methods of rotating a shaft by hydraulic means include the linear actuator and crank arm system which has the disadvantage that the angle of rotation is limited to little over 90.degree.. Furthermore, the velocity and power output varies significantly due to the increase and decrease in the crank arm's perpendicular length.
Another system for rotating a shaft about a pivot point is the rack and pinion actuator which does provide constant velocity and power output but is expensive to manufacture and has poor shock load capacity because the entire reaction force is against one tooth.
The vane-type actuator offers constant velocity but is also expensive to manufacture and suffers from inability to hold a load because of high leakage rates. Furthermore, the vane actuator is unable to sustain end of stroke shock loads.
Another prior art method of rotating a shaft about a pivot point is the linear actuator and chain drive which possesses the low cost benefit of the linear actuator and the constant velocity of the rack and pinion by using opposed cylinders to pull a chain which is engaged in a sprocket. However, this arrangement requires a very large space because of the extended length of the cylinders.
It is therefore, an object of the invention to provide an improved rotary hydraulic actuator for rotating a shaft around a pivot point which provides 180.degree. of rotation.